1. Field of the Invention
The present invention concerns a suspension device for a rotary support arm of a vehicle wheel, in particular for a motorcycle wheel, the said support arm being adapted to rotate reciprocally about a connecting axis integral with the chassis or the body of the vehicle in order to cooperate with a compression spring. The invention also concerns a frontrear coupling system for such a suspension.
2. Description of the Prior Art
The suspension of vehicles by means of rotary suspension support arms for each of the wheels is well known, in particular in the field of suspension of automotive vehicles where the rotary arm is advantageously rendered integral in rotation with one of the ends of a torsion bar the other end of which is anchored in the chassis of the vehicle. These compact and practical provisions cannot unfortunately be applied to motorcycles where there is insufficient width to transversally house a torsion bar spring.
In the field of motorcycles, the suspension spring is generally helicoidal spring incorporated about a hydraulic shock absorber jack and the shock absorbing and/or flexibility characteristics thereof are rapidly adjustable through the intermediary of notches or screws. The reciprocating displacement of the rotary support arm at the point of hinging of the suspension levers is furthermore amplified by levers at the bearing end of the compression spring, this amplification being exerted with variable rates as a function of the compression of the suspension so as to stiffen the suspension progressively as it is compressed, thereby reducing the risk of sudden jolts.
These amplification devices of variable rate stroke according to the compression of the suspension considerably complicate the system. On the other hand, the coupling of the front rear suspensions of a vehicle and substantially modify the interaction between the suspension spring and the shock absorber. It would thus be desirable, both for adjusting more easily the shock absorbing characteristics and to be able to connect the front and rear suspensions of a motorcycle, in order to reduce the swaying and the diving or "leap" of the front axle upon braking, to provide a front and/or rear suspension where the compression stroke of the suspension spring in the form of a helicoidal compression spring is amplified but in a way substantially proportional to the compression of the suspension or at least to the rotation of the wheel support arm.